Патент USA US2129841код для вставки
Patented Sept. 13, 1938 2,129,841 . UNITED STATES PATENT‘ OFFICE 2,129,841 _ COLORED SILICATE COATING Carl E. Hillers, Charlottesville, Va., assignor to Blue Ridge Slate Corporation, Charlottesville, Va., a corporation'of Virginia No Drawing. ‘ Application March 21, 1935, ' Serial No. 12,255 8 Claims. This invention relates to new and useful immovements in colored silicate vcoatings on re fractory granular material. The object of the present invention is to pre 5 vent or to diminish the tendency of such coatings to bloom. Blooming is a characteristic defect of many types of coatings produced from sodium silicate, and I accomplish my object by incor porating boric acid or boric oxide with the sodium 10" silicate in the coating of the granules, thus pro ducing under proper heating conditions a marked reduction in ‘carbonate blooming tendency. Fur (0]. 91-70) sodium silicate that it loses its adhesive quality. If a saturated solution of boric acid is added, precipitation ‘occurs and, due to dilution, the so ' dium silicate loses much of its adhesive quality. As the addition is continued, and sometimes 5 merely upon standing, gell formation takes place. Granules coated with such gells will not make a satisfactory commercial product unless they are processed~ at high temperatures, preferably around the flux point of the coating. 10 On account of the limited solubility of boric acid in water, even a saturated solution would add excessive water to the sodium silicate. Granules. thermore, the water solubility of my coatings is materially .reduced as compared to ordinary ' unless very porous, when coated with dilute so T5 silicate coatings. dium silicate will usually show poor color devel ' Granules coated in accordance with the pres ent invention may be used as a surfacing for asphalt shingles and for other decorative or ornamental purposes. . In the following discussion the term “sodium silicate" usually designates an aqueous solution of speci?c gravity 1.40 to 1.43 of the neutral sili cate of commerce which is composed of NazO and SiO: in the‘ molar ratio of approximately 1 to 3.25,v 25 and contains about 38 to 39 per cent of. solids, ' i. e.,non-volatile. ' -. . One theory which has been advanced to ex plain the e?iorescing tendency of the usual sodium silicate granule coatings is that the SiOz opment. ' _ If dry, powdered boric acid in the amount of _ 0.5 to 1.0 grams be added to ten grams of sodium silicate, precipitation occurs immediately. Owing to this well known phenomenon, these substances are generally considered as incompatible. -If stirred, the mixture becomes full of gritty lumps and may even assume 'a solid form. Such mix tures cannot be uniformly distributed over'the ‘surfaces of refractory granules. ' 25 I have found, however, that by causing this re action to take place on the surfaces of refractory granules, and subsequently heating the granules, uniformly coated granules will be produced which 30' portion of the coating is so weakly acidic that it have excellent qualities as far as bloom and allows sodium hydroxide to form by hydrolysis which then combines with the carbon dioxide of the atmosphere. According to another theory, weather resistance, water insolubility and adhe siveness‘to asphalt shingles or the like are con cerned, particularly ‘where coloring material is incorporated in the coating. The colored coatings on such granulesundergo certain color changes during the heating process. They lose water and the boric acid undoubtedly passes through the stages of metaboric acid, tetraboric acid, etc. I consider 600° F. approxi mately the lower heating limit ‘required for Weather resistance in such coatings when applied carbon dioxide (or carbonic acid) is more strongly acidic than silicon dioxide (or silicic acid),.and in the presence of moisture the carbon dioxide dis places the silicon dioxide from combination with the sodium oxide or hydroxide. Without accepting or rejecting these theories, ~10 I ?nd that the presence of carbon dioxide in ef— ?ores'cence can usually be demonstrated quite easily by treating it with a drop of hydrochloric acid. ‘ The absorption of atmospheric carbon dioxide 45 by sodium silicate could be prevented by the addi tion of the proper amounts of acids stronger than carbonic acid. to most granular bases. The colors are clean and bright. As the temperature of the heat treat ment is raised the color progressively lightens, and will be lighest at 1200-1250n F. The color will darken as the temperature is increased to 1300 However, uponthe addition of 1350° F. and even up to 1500° F. in some cases. even the weakest acids to sodium silicate, either precipitation or gelling usually occurs. This ap plies also to boric acid. If boric acid in dilute solution is added to sodium silicate at ‘room tem At higher temperatures, up to 1800-1900° F. the color will again lighten. Of course, the above perature, there is no apparent immediate action, though gelling may occur later, but the quantity of water required to introduce an appreciable 55 amount of boric acid in this way so dilutes the 15 ' mentioned temperatures are the maximum at— tained during the heat treatment, and these color variations are observed only after the cooling of the granules. ' ‘ The melting point of boric acid is about 365° F. The starting material, orthoboric acid, loses water 55 ' aiaasu .2. of constitution at 212° F. and changes'progres" sively at higher temperatures, ultimately yield ing boric oxide. Orthoborlc acid, as well as the intermediate heat products up to and including boric oxide, are all quite soluble in hot water. Granule coatings comprising only boric oxide or boric acid, unless heated to fairly high tempera tures, have little or no weather resistance andv are easily dissolved in hot water. '10 v Sodium silicate coated granules are also soluble in hot water in inverse ratio, roughly, to the tem perature of their heat'treatment. I Refractory granules coated with sodium sili cate and boric acid together not only bloom less 15 and much more slowly, but are much less soluble upon protracted extraction in hot water than like granules coated with sodium silicate. In practicing my process, I proceed to mix the ingredients in one of a number of different ways, 20 ‘three of which I_ shall now describe on a labo ratory scale,_using small quantities of materials, a small container and a wooden stick for stir ring. In all three methods I shall use the same formula, consisting of granular mineral mate-' 25 rial such as - Grams Slate- _ 100 the latter occur, bare or uncolored surfaces will appear in the granules after the heat treatment, reducing their attractiveness, or at least the uni formity‘ of their color effect, and .this is usually undesirable. Although I have speci?ed one-half minute in the examples, I do not wish to limit my process in its application to that exact time, since I find that the length of time is also re lated to the vigorousness and efficiency of ‘the mixing equipment. In production, I find that from 30 seconds to ' 45 seconds mixing in a Stedman mixer (2 ton capacity) charged with one ton of granules, driven at 71/2 revolutions per minute produces the desired coating. The 30 to 45 seconds of 15 mixing refer only to the stage where the sodium ‘silicate and the powdered boric acid are being mixed on the granules, and not to the total _mix ing time, which may vary considerably depend ing upon the method employed and the order in 20 which the various ingredients are added. Al though I have shown three methods for mixing, it will be evident to one versed in the art that other variations are possible; consequently I do not wish to limit myself to any mixing method or mixing devices or any maximum or minimum amount of time employed therein, for I consider ' Chrome oxide ____ _'_ __________________ __ _ 0.75 that my, invention covers broadly all processes Dry, powdered boric\acid.. _________ ____'__ 0.25 of manipulation substantially equivalent to the 5.0 treatment described. 30 Sodium silicate____-_ _________________ __ I It will also be evident that one mixing method Mixing methods may be better adapted than others to granules (A) Pour the granular slate into ‘the container and add the boric acid. Stir thoroughly for, say, 35 two minutes. Then add the chrome oxide and stir for about 1/2 minute. Then add the sodium silicate and stir vigorously for about 1/2 minute. Proceed to heating treatment. (3) Pour the granular slate, the chrome oxide’ of a certain nature, and that the method best adapted to one kind of granules need not neces sarily be best adapted to all kinds of granules, and, further, that two or more of the methods given may produce approximately equal results on one kind of granules.- On account of varia tions in any one type of stone (or type of brick, or slag or speci?c minerals, etc.) depending and the sodium silicate together. into the con tainer and stir; for from 1/2 minute to 3 minutes upon geographic occurrence, method of crush or longer (or, alternatively, mix the chrome ox ' ing, etc., it is quite impossible here to lay down hard and fast rules for the particular mixing ides and the sodium silicate into a roughly dis persed paint, add this to the slate granules and method or‘modi?cation thereof best adapted to stir for from‘ 1/2 minute to 3 minutes or longer). each kind of refractory granular base, but from 45 my experience I know that at least one of the Then add the powdered boric acid and stir vigor ouslyfor 1/2 minute. Proceed to heating treat ment. ' (C) First stir together for about 1 minute the 50 sodium silicate and the chrome oxide in the mix-' ing container (or in a separate container) to produce a roughly dispersed paint. Then com bine this paint, the slate granules, add the pow dered boric acid in the mixing container, and 55 stir vigorously for 1/2 minute. Proceed to heat ing treatment. , ' In practice, method C occurs usually as a ' combination of methods A and B wherein some of the individual granules are first coated with sodium silicate and subsequently coated with boric acid and other individual granules are ?rst coated with boric acid and then with sodium silicates. . In the examples illustrating the type of mix 65, ing procedure I use, several variations and modi ?cations are shown, but in all three methods the length of time the sodium silicate and powdered boric acid are ‘mixed together on the granules is one-half minute. This is an important feature of my process, because too short‘ a mixing time results in incomplete distribution of the boric acid in the sodium silicate, whereas too long or .. too much mixing results in scraping the wet oo agulatedlcolored coating o?! some of the surfaces of certain percentage of the granules. Should methods will produce well coatedgranules by my process on any refractory granular base. Other methods of combining sodium silicate and boric acid may also be practicable. A solu 50 tion of boric acid may, for instance, be appliedv to the base and then dried before the application of the sodium silicate. In such casesthe boric acid should be dry or nearly dry when the so dium silicate is applied. - 55 My process could be applied to hot slag or other heated granules by ?rst diluting the so dium silicate with su?icient water to allow the granules to be quenched and cooled thereby, while still maintaining ‘some of the sodium sili cate on the surface moist, and then rapidly mix 00' ing on the boric-acid. Other methods will occur to those skilled in the art. Coloring matter may be added along with the sodium silicate or later, as desired. " ’ ' . 65 Heat treatment Pour the ‘wet mixed granules mixed in accord ance with methods A, B, or C into a metal dish (or tray) or the like. Preferably the tray should be hot. Transfer to a furnace,‘ and stir occa sionally with-a long metal handled, wide, single toothed’ rake to prevent caking of the granules during the early stages of the heating. The fun nace is preferably heated to a temperature slight- 75 3 2,129,841 lyvhigher than desired before introducing the tray of granules, so that the granules will quickly come to the desired temperature, and thus ' the total heating period need not exceed ten minutes. Usu ally only ?ve to seven minutes are required. At the end of the heating period, remove the tray of granules ‘from the furnace and allow the gran of at least 600° F. is necessary in my' process to produce colored coated granules with good weath ering properties, there are certain blast furnace slags which may produce colored coated granu lar material with good weathering properties in my process at temperatures below 600° F. during ules to cool, either in the tray in air, or by cooling the heat treatment, and I ?nd that such granules possess less tendency to e?loresce than‘if made in the bottom of the tray in water, or by pouring accordance with other methods. 10 from the tray to an air-cooled or water-cooled surface of metal or stone. If desired, water may be sprinkled on the hot graniiles to assist in cool ing, but the amount of water thus used should not be excessive. ' Otherwise the granules will be wet 15 when cooled and will have to be dried afterwards. The temperatures I employ during the heating ' Although in the mixing examples, I have de scribed slate as the granular base material, I do not wish to restrict the application of my process to slate. U! 10 I ?nd it is adaptable to many other granular bases of a refractory character, whether of mineral or ceramic origin. For some of the applications of my coated granules, I ?nd other treatment depend upon the color desired in the ' bases are even better suited than slate. For ex ?nal product. 'If the slate granules mixed as in ample, I may use this coating in coloring dust A, B or C be heated for ?ve minutes'at-a tem >free sand to be used in children’s play boxes, for, 20 perature between 600° F. and 1200° F., the color when colored, it provides an attractive material of the cooled granules will be of a pleasing yel of greater insolubility in water than ordinary sili lowish-‘green or bluish-green shade. Tempera cate coated granules, and is free from any dan tures below 1000° F. tend to produce the yellow gerous or harmful ingredients, such as uncom-v ish-green colors, being more intense at the lower bined lead compounds, etc., which may occur in some types of glass-coated granules. The gran 25 25 temperatures and gradually changing to the blu ish~green at' the higher temperatures. Thus, by ules are quite free from dust. controlling the temperature, (all other factors be Other granular refractory bases which I have ing equal) the color maybe maintained quite uni employed include feldspar, sandstone, limestone, form, or various colors may be produced from the '30 same formula simply by establishing different temperatures for the heat treatment. If the temperature employed during the heat treatment exceeds about 1250“ F., further changes in color occur,‘ tending to darkenthe shade of 35 green, of the product as the temperature is raised. In my heating equipment, wherein the pyrometer tip is located about one inch above the surface of the granules in the tray, this darkening of ‘ shade appears noticeable about 1280° F. and be comes more pronounced at higher temperatures, such as 1400° F. or 1500" F. Above this tempera ture, the hot granules assume a sticky condition traprock, shale, quartzite, brick, broken glass, greenstone, granite, slag, quartz, basalt and dia 30 base, and I ?nd that practically anyrefractory rock can be color-coated by my process, although all bases are not suitable for producing the same color. The choice of base provides further varia tions in color effects from the same formula, and 35 unless the granular base tends too greatly to dis integrate or in other ways to change during the mixing or heat treatment or afterwards, nearly any base, within reason, may be used to produce colored granular material of commercial value by 40, my process. ' Some slates are too greatly changed by heating noticeable if raked, and melting of the coating above 1500° F. to have colorv appeal, but’ even, occurs. When a granular base such as sand is these I ?nd can be greatly improved in color, 45 used, this molten coating assumes a condition of sticky fluidity or sloughing, and if the temperature using the same total amount of coloring principle is further raised above 1600°_1750° F., the vfluidity by a double coating and double heating operation. may gradually diminish and the heated granules The heat treatment employed on the ?rst coating may show a tendency to become crusty. Upon need not be above 1100° F. to provide greater re 50 cooling, such granules may be light in color and jsistances in the second coat to heating in the 1500“ F. and above temperature range. Certain more desirable for some uses than either the gran ules prepared by heating in the ranges 600° to ‘ “greenstone," granite, limestone and traprock 1200° F. or 1200° to 1600° F. bases likewise are not suited for heating above In heat treating on a manufacturing scale gran 1000° F. when attempting to produce some colors 55 ules coated and colored as above described, I may use an inclined rotary kiln for a continuous proc ess, or other types of heating devices if “batch heating” is preferred. I do not wish to limit my process to any particular heating ‘device. I prefer, 60 however, that the heat treating devices be so designed and operated as to provide either expo sure of the granules to heat in thin layers or agi - tition or rotation to insure uniform heating. Co because of color changes in the base material or for other reasons,‘ but the colors produced by heating to temperatures at which the rock is stable, may be very desirable. In the preceding examples, I have used pow dered boric acid and sodium silicate in the pro 60 portions of 5 lbs. of the former and 100 lbs. of the latter per ton of granules. I have found that the proportion of materials may not vary greatly in hesion between the coated granules while wet is not an obstacle that must be overcome mechan my process, if the desired results are to be ob tained. I This is especially true if the subsequent ically, since granular material coated in accord heating treatment of the coated granules is con ance with my invention as distinguished from ducted below the ?uxing point of the coating. To - ' “silicate granules” has less tendency. to ball up or form lumps during the early stages of the produce boric acid-sodium silicate coated gran ules which are substantially free from the tend heating process. ency to form a ‘carbonate bloom, three or four "T: I do not wish to limit my process to speci?c tem peratures. The temperatures employed should not be suf?ciently high completely to fuse the granular base material.- Although on “most min‘. .75 eral material of natural origin, a temperature percent of boric acid on the weight of the sodium silicate per ton of granules is necessary. Smaller amounts exert a correspondingly smaller effect. More than ten percent of boric acid appears to ‘alter the relationship necessary between boric 76 4 perature at which they have been previously heat acid and sodium silicate for good weather resist ing colored granules, and I have not found ' treated, and the fact that granules prepared by higher boric acid percentages of any particular my process show decreased total extractible solu value in my process, regardless of the tempera ture employed. However, since the amount of ble salts, indicate that my process produces a coating imwhich the sodium (or NaaO) is more sodium silicate used per ton of granules may be ?rmly held than in silicate coatings. This is varied, depending upon the kind of granular base ' borne out also by the greater resistance to bloom used, the shape, porosity, and size of the indi vidual granules and whether one or two or more of my coatings. Disregarding solution of, or chemical reaction coats be applied thereto, etc., I prefer to express with coloring agents, my process results in “so 10 boric acid used, based on the weight of sodium other coloring matter will give a satisfactory sodium-boro-silicate coating only if heated to a 15 the relationship, not in terms of pounds or per- _ dium-boro-silicate” coatings on the granules; hence, I refer to ‘the product as “boro-silicate 'centages of boric acid per ton of granular ma terial, but in terms of the percentage of powdered granules.” Borax, silica and chrome oxide or 15 silicate employed. This relationship, calculating boricLacid as 56.4% non-volatile, and sodium silicate as being approximately 40% non-volatile, and comprising one part NaaO to 325 parts of Si 02 is as follows: 20 relatively high temperature, above approximately 1300° F. My coating having the above desired qualities can be produced at any temperature above 600° F., or with certain bases, even lower. This results in great fuel economy and a much 20 wider choice of granular base. Also coating ma-, Percent by weight terials consisting of silica, chrome oxide, boric 25 B203 N830 Si 0: Percent Percent Percent Minimum ________________________ _. 4. 23 24 Maximum _______________ ___ _______ __ 14. 10 24 1 acid or boric oxide and sodium hydroxide or so _ 76 ' dium carbonate would produce a sodium-boro silicate coating only if heated to 1300 F. or 25 higher. ' _ 76 What I claim is: 1. The process'of coating granules of refrac The minimum percent of B203 (4.23) is equiva tory material comprising the following .steps: lent to 3 lbs. of powdered boric acid‘per 100 lbs. mixing together sodium silicate and chrome oxide 30 30 of sodium silicate, and the maximum (14.10) is to produce a roughly dispersed paint, mixing to equivalent to 10 lbs. of powdered boric acid per gether the paint, the granules and powdered boric 100 lbs. of sodium silicate. For practical pur acid, and heating the coated granules. poses I ?nd that from four to six percent of boric acid on the weight of the sodium silicate is both 85 economical and effective, yetit will‘be evident 2. The process of coating granules of refrac- tory material comprising the ‘following steps: mixing the granules, sodium silicate and color 35 that slight departures from my maximum and ing matter together uniformly to-coat the gran- ' minimum amounts maybe used without depart— . ules, then applying to the wet coating on the ing from the spirit of my invention. . _ surfaces of the granules dry, powdered boric acid, Although I have illustrated with a sodium and ?nally heating the granules. 40 40 silicate solution of approximately 40% solids, in 3. The process of coating granules of refractory which sodium oxide and silicon dioxideare pres material comprising‘ the following steps, mixing “ ent in the ratio of approximately 1:3.25, it will the granules and sodium silicate together uni be evident that solutions‘of other solids content, formly to coat the granules, mixing with the such as 35% solids or less up to 512% solids or coated granules dry, powdered boric acid, and 45 slightly more, wherein the solids may consist of sodium oxide and silicon dioxide in ratios rang ing from 1:3.0 up to 1:4.0, may be used without departing from the spirit of my invention. In the examples I have used chrome oxide as the color principle. I do not wish to restrict my self to the use of any specific color principle, nor to any particular amount of color principle, since a wide range and variety of color imparting ma terials may be used alone or in combinations, in ‘ eluding ultramarines, metal oxides and other compounds, themselves stable colors or capable of being converted into colored oxides or stable forms of colored materials under the coating and/or heating treatment, etc. The decreased solubility of coatings on gran ules produced by my process as compared to sili cate coatings prepared under the same condi tions (same base, same mixing time, same heat ing operation, etc.) indicates that the coating produced by my process is not merely a silicate coating. Boric acid is a water soluble substance, and I find that extraction in distilled water for twelve hours at 175° F.’ or higher, will dissolve a relatively large quantity of it. Silicate gran .70 ules likewise show a distinct solubility during twelve hours extraction, depending upon the tem heating the granules. ’ 4. The process of coating granules of refraca tory material comprising the following steps: uni formly coating the granules with sodium silicate and pigment, mixing the coated granules with dry, powdered boric acid, and heating the gran ules. 5. The process of coating. granules of refrac tory material comprising the following steps: coating the granules with pigmented sodium sili cate, mixing the coated granules with dry, pow~ dered boric acid, and heating the granules. 6. The process de?ned in claim 5 and in which the relationship between the ingredients is as fol lows, expressed in per cent by weight: B20; 60 4.234410%, NazO 24%, S10: 76% or approxi mately 3-10 lbs. of powdered boric acid per 100 lbs. of sodium silicate. '7. The process de?ned in claim 5 and in which the weight of the powdered boric acid is less than 10% of the weight of the sodium silicate. 8. The process de?ned in claim 5 and in which the weight of the powdered boric acid is 3-4% of the weight of the sodium silicate. '/ [CARL E. HILLERS.